Section 99H. The director of accounts in the department of revenue shall annually cause an audit to be made of the accounts of the regional police district commission, and for this purpose he, and his duly accredited agents, shall have access to all necessary papers, books and records. Upon the completion of each audit, a report thereon shall be made to the chairman of the selectmen of each town which is a member of the district. The director shall apportion the cost among the member towns on the basis provided by section ninety-nine I, and submit the amounts of each apportionment to the state treasurer who shall issue his warrant requiring the assessors of the towns which are members of the district to assess a tax to the amount of the expense, and such amounts shall be collected and paid to the state treasurer as provided by section twenty of chapter fifty-nine.